Sweetening process



Patented Apr. 15, 1930 GENTRY' LLOYD ROWSEY, F AiMARILLO, TEXASSWEETENING PROCESS N0 Drawing. Application filed April 13,

This invention relates to the refining of hydrocarbon oils; particularlyto improvements in the refining of oils of the gasolinekerosene type.

In refining gasolines and kerosenes, it has been common practice .toagitate these oils with solutions containing litharge dissolved in anexcess of caustic soda. Such alkaline solutions of sodium'plumbite form'certain colored lead compounds which are oil-soluble but which areprecipitated by the addition of free sulphur. To the extent to which thetreated oils may contain elementary sulphur, such oil-soluble leadcompounds may be precipitated by this sulphur. In practically all cases,however, it is necessary after agitation with the alkaline sodiumplumbite solution, to add free sulphur to break up these 011- solublecolored lead compounds and to effect the removal'of lead so combined aslead sulphide. This operation is commonly called sweetening. There areseveral Well recog nized difficulties incident to the method ofsweetening just described. The cost of the reagents is frequentlyexcessive; as much as a pound of litharge per barrel of gasoline orkerosene treated may be consumed 1n the operation. It is diiiicultaccurately to regulate the addition of free sulphur to the 011;

usually a slight excess of free sulphur is left in the oil resulting incolor instabillty and causing the oil to be corrosg e w th respect tometals such' as copper; brass or bronze.

The precipitate formed in the Oll by the add1- tion of sulphur, largelylead sulphide, is at first extremely flocculent and voluminous andretains a considerable proportion of the oil.

Much time is lost in effecting settling of these pgecipitates in orderto permit a reasonably c mplete separation of the ml, and even underfavorable conditions there 1s usually a substantial loss of the refinedoil product in the precipitate. This precipitate is commonly discarded,although in some instances it 1s treated for the recovery of litharge orsodium plumbite to be used in subsequent operations.

Other sweetening methods have been proposed; for example there havebeenproposals to eiiect the purpose of the sweetemngoperation byoxidation'of the objectionable com- 1927. Serial No. 183,624.

pounds, mainly sulphur derivatives, by various oxidizing agents and byabsorption of such objectionable compounds on various absorbentmaterials such as silica gel, bauxite or absorbent precipitates formedin the oil. In general, however, the alkali plumbite method has beenmost generally used. My invention has several important advantages overthis common alkali plumbite sweetening operation.

According to my invention, the gasoline or kerosene is treated with asolution of'caustic alkali containing suspended preformed lead sulphidewhile subjected to the action of air brought into intimate contact withthe oil and treating solution. In carrying out my inven tion, it isadvantageous to mix the oil and treating solution together while blowingair therethrough under conditions such that the air is intimatelydistributed through themixture in the form of fine bubbles. It is alsoadvantageous to employ a treating solution containing suspended a densepulverulent form of lead sulphide.

Lead sulphide precipitated in the usual sodium plumbite sweeteningoperation changes from the bulky flocculent form in which it isinitially precipitated to a fine, dense powder-like material afterstanding for some time. This more dense material quickly settles out ofoil with which it is agitated. I have found this relatively densepulverulent form of {lead sulphide, formed when the pre cipitate theordinary sodium plumbite sweetening operation is permitted to stand, isa particularly advantageous form of lead sulphide for use in-carryingout=my present invention. I

I have found that even extremely malodorous gasolines or kerosenes,containing for example sufficient sulphur containing impurities of themercaptan type to have a very ob j ectionable odor and topause largeconsumption of sodium plumbite in the ordinary sweetening operation,"can. be rendered entirely satisfactory as to odor and non-reactive tothe sodium plumbite reagent in a very brief. period of treatment byagitation with a suspension of lead sulphide in a caustic alkalisolution in the presence of air introduced into and passed through theoil and treating solution in the form of fine bubbles. Subsequent tothis treatment, the lead sulphide suspension is settled out of the oil.This settling is easily and quickly effected if the form of leadsulphide described above is used.

The alkaline suspension of lead sulphide separated from the oil aftertreatment can be used again for treatment of further quantities of theoil, and the activity of the lead sulphide apparently continues for anindefinite time. In the practice of my invention on an industrial scale,I have employed the same alkaline suspension of lead sulphide forperiods of three or four weeks in the continuous treatment of successivequantities of raw gasoline without having to replenish the leadsulphide. vantages of my invention; there is no large consumption of theactive material, and this affords an important economy as compared tomethods hitherto known, in which litharge used for example.

I have found that intimate contacting of air with the lead sulphidesuspension is essential, and that the effectiveness and rapidity of thetreating operation is to a large extent promoted by promoting intimatecontact between the mixture of Oll and the treating solution and the airsupplied to the operation.

I have also found that it is advantageous to use treating solutions freefrom dissolved litharge; otherwise there is sometimes a tendency towardformation of the oil-soluble lead compounds to which I have previouslyreferred. Such compounds, 'if formed, can be decomposed or oxidized byprolonged treatment, but I have found it advantageous to carry theoperation out in the substantial absence of sodium plumbite to avoid anyformation of such components.

The caustic soda in the treating solution is consumed by the action ofany dissolved hydrogen sulphide present in the oil subjected totreatment, and I have also found that the resulting alkali sulphides inthe treating solution apparently retard the sweetening operation ifpresent in sufficient amount. Accordingly, I find it advantageous togive oils containing dissolved hydrogen sulphide a preliminary treatmentwith a caustic olution, for example with a solution containing theminimum proportion of caustic soda sufficient to remove such dissolvedhydrogen sulphide.

As a specific example of the practice of my invention. I give below anoperation carried out upon a very sour gasoline obtained from crudepetroleum from the Panhandle field in Texas, commonly known as Panhandlecrude:

The gasoline treated had a particularly high content of sulphurcompounds of the mercaptan type, and when treated by the usual sodiumplumbite method required about one pound of litharge and acorrespondingly large proportion of sulphur per barrel (42 This is oneof the important adgallons). In a batch operation, in accordance with myinvention, 1,000 barrels of this gasoline were treated with 100 barrelsof a solution of caustic soda, about 15 B., containing about 1,500pounds of previously prepared precipitated lead sulphide in suspension.This mixture was agitated by blowing air through it, and the air wasintroduced so as to form fine bubbles producing a froth which wascarried up into and through the oil. After fifteen minutes agitation,the treating solution and suspended lead sulphide was allowed to settleout of the oil, and the oil separated from the settled alkaline mixture.The separated oil was of entirely satisfactory odor and was non-reactiveto sodium plumbite.

In the treatment of such gasoline in the manner just described, it isnot unusual to find that there has also been a substantial improvementin color, for example as much as one to two points on the Saybolt colorscale.

I have observed, in *arrying out my inven tion, that the bubbles of airwhen in a sufficiently line state of sub-division, become filmed overwith lead sulphide, the lead sulphide thus being carried up through theoil. And I find it advantageous in carrying out my invention to promotesub-division of the air introduced into the mixture of oil and treatingsolution. For this purpose, I have employed various forms of apparatus.For example, in the treatment of successive batches of oil, I haveemployed cone bottom agitators of conventional design and haveintroduced the air in very fine streams of bubbles through a pluralityof small orifices arranged close to the bottom of the cone. I have alsointroduced the air in relatively small streams beneath mechanicalagitating devices such as a propeller or a propeller arranged to operatewithin a sleeve. The air may also be introduced by forcing it into themixture of oil and treating solution through porous material, forexample through a tube or plate of alundum or porous baked silica,forming very fine bubbles or a fine froth. In continuous operation, theoil and treating solution may be supplied to the lower end of avertically arrange-d orifice mixer into the low-er part of which thenecessary air is also introduced.

I am not certain as to the exact relationship of the effect of'the airand the metallic sulphide in the calistic soda solution in causing thesweetening action. The air and lead suI- phide apparently react to aconsiderable extent to form sodium thiosulphate, which then reacts withthe sulphur compounds in the oil to assist in the sweetening action.There also appears to be a direct oxidation of the sulphur compounds bythe air when intimately admixed with the oil being treated, the leadsulphide promoting the reaction. In any event I do know that the actionof the air on the lead sulphide suspended in the caustic soda solutionor on the oil in the presence of the lead sulphide suspension is suchthat the desired result is accomplished in a period of time in whichthere seems to be very little if any improvement in the absence of leadsulphide. However, I do not intend to predicate my invention upon anyparticular explanation. I may also note that the treatment of gasolinesand kerosenesin accordance with my invention does notusually involve anylarge reduction in sulphur content.

In commercial practice, I have found that, even in extreme cases, theuse of inordinately large volumes of air is unnecessary. In many cases,for example, I have found the total volume of air required is not muchmore than about ten times the total volume of the oil treated, andfrequently the proportion required is less than this. The proportion ofair used, of course, is dependent upon the efficiency with which it-isused, and this is another respect in which fine sub-division of the airassists in making the operation economical.

My invention also lends itself to continuous operation. In continuousoperation, gasoline or kerosene is pumped continuously through a zonewhere it is intimately mixed and agitated with the treating solutioncontaining lead sulphide and caustic soda and with air and is thenconducted through one or more settling receptacles where the rate offlow is adjusted to promote separation of the oil from the treatingsolution. The facility with which the treating solution can be caused toseparate from the oil in carrying out my in vention makes itparticularly valuable for continuous operation. ikewise, in continuousoperation in accordance with my invention, the treatedsolution'containing lead sulphide may be pumped directl from the bottomof the settling tanks bac to the mixing apparatus. The treatingsolution, in such an operation, may be replaced from time to time, or apart of it may be continuously discharged and this part replaced byfresh treating solution.

In order to reduce any loss of gasoline or kerosene by evaporation, theair employed is advantageously recirculated, in whole or in part, untildue to consumption of oxygen it becomes ineffective for the purposes ofthe treatment. Likewise, escaping air may be subjected to treatment forthe recovery of any hydrocarbon vapors it may contain, for

example by absorption treatment with active charcoal or with anabsorbent oil, or-by cooling and compression. Although the lead sulphidem be used repeatedly, an indefinite number of times, its activity may bepromoted by treatment, from time to time, with steam to remove anyabsorbed or entrained oils or oily impurities.

Such treatment assists in making it ossible to use a minimum of the leadsulphide or to reduce the time of treatment or to reduce the amount ofair required.

I claim:

1. An improved method of sweetening gasolines and .kerosenes whichcomprises agitating the oil With a suspension of preformed lead sulphidein a caustic soda solution while bringing air into intimate contact withthe mixture.

2. .An improved method of sweetening gasolines and kerosenes whichcomprises agitating the oil with a suspension of dense pulverulent leadsulphide in a solution of caustic soda while bringing air into intimatecontact with the mixture.

3. An improved method of sweetening gasolines and kerosenes whichcomprises agitating the oil with a suspension of preformed lead sulphidein a caustic soda solution while passing air through the mixture in theform of line bubbles.

4. An improved method gasolines and kerosenes which com rises agi tatingthe oil with a suspension 0 lead sulphide in a solution of caustic sodasubstantially free from dissolved litharge while bringing air intointimate contact with the mixture.

In testimony whereof I afiix my signature.

GENTRY LLOYD ROWSEY.

of sweetening

